72 



FOUNDATIONS OF BIOLOGY 



what modified at the point of union with the stem into a 

 LEAF BASE from which arise leaf-like appendages, or STIP- 

 ULES. When the petiole is absent the lamina of such a sessile 

 leaf appears to arise directly from the stem. 

 (Fig. 34.) 



The leaf, like the root and the stem, ex- 

 hibits numerous modifications in adaptation 

 to other functions. The chlorophyll-bearing 

 tissue may be nearly or completely sup- 

 pressed, as in the SCALES which 

 enclose winter buds in a pro- 

 tective case. These are con- 

 spicuously developed in the 

 Horse Chestnut and the Hick- 

 ory. (Fig. 35.) Or the scale 

 leaves, in addition to affording 

 protection, may act as reser- 

 voirs in which food materials 

 are stored, an example of 

 which is the familiar Onion. 

 (Fig. 36.) All transitions be- 

 tween scale leaves and typical 

 foliage leaves may frequently 



FIG. 35. Shoot . . < i T i r 



of Horse chestnut be seen in an unfolding leaf 



sea 



bud. Still more marked de- 



FIG. 36 Onion 

 leaf, cut longitudi- 

 nally, bl, blade; 

 int, hollow interior 

 of blade; s, thin 

 sheath of leaf; 



showing winter 

 buds enclosed by 



thick scale leaves; partures from the usual leaf- 



k, small axillary r ,i e <snrnp sea, thickened base 



bud; x, scar of leaf IOrm are 



of previous season. c li m bing plants such as the 



(From Campbell.) ' 



Sweet Pea, the SPINES of the 

 Barberry and the Thistle, and the 'insect traps' of Pitcher- 

 plants and Sundews which capture small living animals. 

 (Figs. 37, 38.) 

 Leaf modification in another direction occurs in the spore- 



of leaf. (From 

 Bergen and Davis, 

 after Sachs.) 



